Turbine casing for a gas turbine engine

ABSTRACT

A turbine casing for a gas turbine comprises a casing defining the boundary of part of the turbine flow duct and formed from a plurality of segments, each segment being mounted from fixed structure by a plurality of radially extending struts. At least some of the struts are arranged to deform to allow relative thermal expansion between the hot segments and the supporting casing with at least one of the struts interposed between the deformable struts being relatively rigid.

United States Patent 1191 1111 3,824,031 Gilbert July 16, 1974 TURBINE CASING FOR A GAS TURBINE 2,863,634 l2/l958 Chamberlin et al. 4l5/2l9 R ENGINE FOREIGN PATENTS OR APPLICATIONS [75 Inventor: g' 'fgg Gilbert Anestree 1,227,668 3/1960 France 4l5/l38 [73] Assignee: f g Limited Primary Examiner-Henry F. Raduazo on an Attorney, Agent, or Firm-Cushman, Darby & [22] Filed: Dec. 29, 1972 Cushman [2]] Appl. No.: 319,763

[57] ABSTRACT [30] Foreign Application Priority Data A b f b i tur me casmg or a gas tur me comprlses a casmg Janv 12, 1972 Great Brltaln 1365/72 defining the boundary of part of the turbine flow duct [52] U 5 Cl 415/135 415/138 60/39 32 and formed from a plurality of segments, each seg- [51] hit Cl 0 d 25 b 25/'26 ment being mounted from fixed structure by a plural- [58] Field 's 60/39 ity of radially extending struts. At least some of the R struts are arranged to deform to allow relative thermal expansion between the hot segments and the supporting casing with at least one of the struts interposed be- [56] E S;?, EE tween the deformable struts being relatively rigid.

841,650 1/1907 .lunggren 415/172 8 Claims, 3 Drawing Figures TURBINE CASING FOR A GAS TURBINE ENGINE This invention relates to a turbine casing for a gas turbine engine.

As the efficiency of gas turbine engines has increased, so the effect of penalties caused by leakages of air both from the main flow annulus and around stages of compression or expansion in the turbine has increased. It is particularly difficult to ensure that there is a sufficiently low amount of leakage around the tips of the turbine rotor stages, since these components are subject to very great difference in temperature between their operative and inoperative conditions.

The present invention provides a turbine casing which allows that part of the casing which forms the outer wall of the main flow duct to remain reasonably concentric and hence enables control of the leakage past the turbine rotor tips.

According to the present invention a turbine casing for a gas turbine engine comprises a plurality of separate arcuate segments which together form an annular casing defining the boundary of the gas flow duct around a turbine rotor stage, each segment being mounted from an outer supporting casing by means of a plurality of circumferentially spaced apart radially extending struts at least the majority of which are adapted to deform to allow relative thermal expansion between the segments and the supporting casing and with at least one strut interposed between the majority being relatively rigid.

Preferably there is a central, relatively rigid strut for each said segment and two further resilient struts equispaced from the central strut.

Said struts preferably extend in a plane substantially parallel to the turbine axis.

Preferably the supporting casing supports the shaft by means of two bearing panels between which the supporting casing extends. In a preferred embodiment there are two sets of said segments carried from one casing extending between two said bearing panels.

The invention will now be particularly described merely by way of example with reference to the accompanying drawings in which:

FIG. 1 is a partly broken away view of a gas turbine engine whose turbine casing is in accordance with the invention,

FIG. 2 is an enlarged section through the turbine of FIG. 1, and

FIG. 3 is a section on the line 3-3 of FIG. 2.

In FIG. 1, there is shown a gas turbine engine comprising an outer casing within which are mounted in flow series a low pressure compressor 11, high pressure compressor 12, combustion section 13, high pressure turbine 14, low pressure turbine and an exhaust nozzle 16. The low pressure compressor and turbine and the high pressure compressor and turbine are respectively interconnected by low pressure and high pressure shafts l7 and 18 respectively. Operation of the engine is conventional in that the compressors 11 and 12 compress the incoming air which is then combusted in the combustion section 13. The resulting gases exhaust through the high pressure and low pressure turbines l4 and 15 hence driving theirrespective compressors and the exhaust gases then flow through the nozzle 16 to provide propulsive thrust.

The engine concerned has a very high pressure ratio and consequently it is necessary to provide adequate sealing between the turbine blade tips and the surrounding casing and this is carried out by the construction shown in more detail in FIGS. 2 and 3.

, In FIG. 2 there is shown the downstream extremity 19 of the combustion chamber of the engine which is attached to a nozzle guide vane 20. A bearing panelis provided which comprises a plurality of separate struts 21 each passing through the hollow interior of one of the vanes 20 from the inner structural casing 22 of the engine. The struts 21 support at their inner extremities a roller bearing 23 which in turn carries the shaft 18.

The nozzle guide vanes 20 are carried on a flange 24 which is bolted to the casing 22 at 25 and which also carries a further supporting cylinder or casing 26 which defines a portion of the structural casing 22. The supporting casing 26 is formed on its inner surface with a plurality of supporting struts 27. The struts are resilient and relatively thin with the exception of the central strut 27 of each set and as can be seen from FIGS. 2 and 3 they extend substantiallyradially and axially of the turbine. Groups of three of the struts 27 each support an arcuate segment 28, a plurality of segments 28 together form an annular casing, generally designated at 28 and which defines an outer boundary of the gas flow duct. Spaced slightly within the segments 28 are the rotor blades 29 of the turbine 14, the blades 29 being carried on a disc 30 which is in turn carried from the shaft 18.

Casing 26 is also provided at its extremity distant from the flange 24 with a further flange 31 which forms the forward support of the stationary guide vanes 32, which are also supported at their downstream end from the structural casing 22. Just downstream of the vanes 32 is mounted the low pressure turbine 15 comprising a plurality of rotor blades 33 mounted from a disc 34 which is carried from the shaft 17.

The tips of the blades 33 lie just inside an annular boundary casing generally designated at 36', formed in a similar way to that of the high pressure turbine. In this case the structural casing 22 directly carries a plurality of struts 35 similar to the struts 27, and once again .groups of three of these struts each support an arcuate segment 36 of the boundary casing 36. In a similar fashion to the segments 28 the segments 36 form the annular casing 36 which is the outer boundary of the flow duct around the turbine blades 33.

Downstream of the turbine blades 33 are mounted a plurality of vanes 37 which are supported from the casing 22. These vanes are hollow and a plurality of struts 38 pass through the hollow centres of the vanes. The struts 38 extend from the casing 22 to form a bearing panel which supports a roller bearing 39 which supports an extension of the shaft 17 and hence the low pressure turbine 15.

Operation of this structure is as follows:

The casing 22 and the shafts 17 and 18 are maintained in fixed relationship with one another by the bearing panels 21 and 38, and the casing 22 and/or 26 is maintained relatively cool. The segments 28 and 36 mounted either directly or indirectly from the casing 22 by their respective struts are hence held completely concentric overall with the shafts 17 and 18. Any relative expansion between the hot segments and the cold casing is allowed by deformation of the outer two resilient struts holding each segment. Although such expansion may produce distortion of each segment, the overall casing will depart very little from concentricity.

Since the concentricity of the casing is thus assured, it is possible to reduce the clearance between the tips of the turbine blades to a very small amount consequently reducing the leakage around the tips of the turbine blades and consequently improving the efficiency of the engine.

It will be appreciated that various modifications could be made. This construction is applicable to any kind of gas turbine engine having a turbine whose tip clearances must be controlled and although its maximum effect is felt with high pressure ratio engines which may have three or more shafts it will still be of advantage to simpler engines. Again it is possible to use other numbers of struts to support the segments although again we prefer to have an odd number so that there may be a central strut and equal numbers either side. 1

I claim:

1. A turbine casing assembly for a gas turbine engine comprising:

an annular support casing:

a plurality of separate arcuate segments spaced radially inwardly of the annular support casing to define an annular boundary casing around at least one stage of a turbine rotor; and means to support each of said arcuate segments from said annular support casing whereby there can be circumferential thermal expansion of said segments and said boundary casing defined thereby relative to said annular support casing, said last-mentioned means including a plurality of circumferentially spaced apart radially extending struts greater than two for each arcuate segment to support the same from said annular support casing, at least one of said plurality of struts is relatively rigid and is interposed between the remaining of said plurality of struts with the same number ofthe remaining struts being on either side of the at least one relatively rigid strut, the remaining of said plurality of struts being resilient and deformable out of their radial alignment to allow for the thermal expansion.

2. A turbine casing assembly as claimed in claim 1 in which each of said plurality of struts extends longitudinally and substantially parallel to the axis of the turbine. V

3. A turbine casing assembly as claimed in claim 1 in which each of said plurality of struts for each arcuate segment is an odd number of struts with the central strut being relatively rigid and the remaining struts being resilient and deformable.

4. A turbine casing assembly as claimed in claim 1 and comprising a turbine shaft supported from said support casing, and two bearing panels between which the casing extends and which support the shaft or shafts.

5. A turbine casing assembly as claimed in claim 4 and in which there are two sets of said segments carried from said support casing extending between two said bearing panels.

6. A turbine casing assembly as claimed in claim I in which each of said plurality of struts for each arcuate segment includes three struts with the central strut being rigid.

7. A turbine casing assembly as claimed in claim 1 including a further annular support casing spaced radially outwardly from said first-mentioned annular support casing for supporting the same.

8. A turbine casing assembly as claimed in claim 1 in which each strut of said plurality of struts for each of said arcuate segments is structurally integral with the respective arcuate segment and said support casing. re-

spective arcuate segment and said support casing. 

1. A turbine casing assembly for a gas turbine engine comprising: an annular support casing: a plurality of separate arcuate segments spaced radially inwardly of the annular support casing to define an annular boundary casing around at least one stage of a turbine rotor; and means to support each of said arcuate segments from said annular support casing whereby there can be circumferential thermal expansion of said segments and said boundary casing defined thereby relative to said annular support casing, said last-mentioned means including a plurality of circumferentially spaced apart radially extending struts greater than two for each arcuate segment to support the same from said annular support casing, at least one of said plurality of struts is relatively rigid and is interposed between the remaining of said plurality of struts with the same number of the remaining struts being on either side of the at least one relatively rigid strut, the remaining of said plurality of struts being resilient and deformable out of their radial alignment to allow for the thermal expansion.
 2. A turbine casing assembly as claimed in claim 1 in which each of said plurality of struts extends longitudinally and substantially parallel to the axis of the turbine.
 3. A turbine casing assembly as claimed in claim 1 in which each of said plurality of struts for each arcuate segment is an odd number of struts with the central strut being relatively rigid and the remaining struts being resilient and deformable.
 4. A turbine casing assembly as claimed in claim 1 and comprising a turbine shaft supported from said support casing, and two bearing panels between which the casing extends and which support the shaft or shafts.
 5. A turbine casing assembly as claimed in claim 4 and in which there are two sets of said segments carried from said support casing extending between two said bearing panels.
 6. A turbine casing assembly as claimed in claim 1 in which each of said plurality of struts for each arcuate segment includes three struts with the central strut being rigid.
 7. A turbine casing assembly as claimed in claim 1 including a further annular support casing spaced radially outwardly from said first-mentioned annular support casing for supporting the same.
 8. A turbine casing assembly as claimed in claim 1 in which each strut of said plurality of struts for each of said arcuate segments is structurally integral with the respective arcuate segment and said support casing. respective arcuate segment and said support casing. 